The substance also was associated with improvements in quality of life and number of relapses, Achiron reported at the annual meeting here of the American Academy of Neurology.

The investigators saw no serious adverse events, Achiron told an oral session, and there was no significant difference between treatment and placebo arms in the number of adverse events.

In particular, calcium levels remained within normal limits in 91.4% of the alfacalcidol patients and 90.2% of those on placebo, she reported.

The compound is a "safe and effective strategy" for treating fatigue in MS patients, Achiron concluded.

The synthetic compound "does look to have activity in MS," commented Robert Fox, MD, of the Cleveland Clinic, who was not part of the study but who moderated a session at which it was presented.

"What's not clear," he told MedPage Today, "is whether there would be similar activity with regular vitamin D."

He said trials with standard vitamin D are now underway and should help settle that question.

Fatigue, Achiron noted, is a daily event for MS patients and is not directly related to depression or the degree of neurological disability. It doesn't respond to current therapies and there is no drug approved specifically for MS-related fatigue.

She and colleagues enrolled 158 MS patients who reported that fatigue interferes with their work, family, or social life, and randomly assigned them to alfacalcidol or placebo for 6 months.

The primary outcome measure was change on the multi-dimensional Fatigue Impact Scale (FIS), with improvement defined as a 30% decrease in the score, Achiron said. Secondary outcomes were improvement in neurological disability, quality of life, and number of relapses.

Participants reported baseline scores of about 80 on the 160-point fatigue scale, where higher scores indicate worse fatigue, she said. But after 6 months, patients in both arms had improvements that were significant at P<0.001.

However, those taking alfacalcidol had a greater relative decrease, on average, than those in the placebo arm -- drops of 41.6% and 27.4%, respectively -- and the difference was significant at P=0.007, she said.

The difference between treatment and placebo was more marked on the cognitive subscale of the FIS, Achiron said, but was still significant for the physical and social subscales.

There was no change in the degree of neurological disability, she reported, but quality of life improved on the psychological and social subscale, although not on the physical subscale.

In the alfacalcidol group, there were eight relapses during the study, compared with 25 in the placebo group (P=0.006).

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